AUSTRALIAN AND NEW ZEALAND DISTRIBUTOR OF X-FLOW SOLAR POOL HEATING KITS
Testing of solar collectors
(3 appendices)
Mission
Development testing of solar collectors with regard to thermal performance in accordance with method NT VVS 004 (SP-C12-301) as well as stagnation tests.
Objects for testing
Texsun solar collectors, modified model since previous report P1 00818_1 with date 2001-04-23. For technical description and pictures of test objects see Appendix 1.
The objects for testing arrived at SP on 2001-04-02, they were inspected and no cause for remarks was found (i.e. they were found to be in normal condition). The testing was performed on 11th and 12th April 2001.
Measuring equipment
| Solar irradiance: | Kipp & Zonen. CM11-871700 SP nr 202185 |
| Temperature: | Temperature sensor Pt-100 (fluid) Etnr.544 and 538 Temperature sensor Pt-100 (air) ETnr.554 and 555 Temperature meter Anritsu HTF-80 SP nr 201452 |
| Flow: | Flow meter Valmet MP 115 SP nr 201574 |
| Air velocity: | Hot-wire anemometer Swema ATD 81S SP nr 200108 |
| Measurement collector: | HP VXI-system |
| Pressure: | Pressure meter Druck DPI 203 SP nr 200638 |
Results
Thermal performance - See Appendix 2
Stagnation test - See Appendix 3
The results given in this report are only applicable for the actual objects tested.
Measurement uncertainty (margin of error)
Total uncertainty for the measured efficiency values depends on the point of operation and is (with 95% confidence interval, k=2) for the highest and for the lowest measured efficiency values:
Umax=+/-0.049 (+/- 4.9% relative)
and
Umin=+/-0.048 (+/- 4.8% relative)
Total uncertainty for the adjustment to a second degree function depends similarly on the point of operation and is (with 95% confidence interval, k=2) for adjusted (revised) value of n0 (U1) and for an efficiency rating calculated with adjusted (revised) n0, k0 and k1 (U2) with half of the maximum over temperature (TF-TL)max/2=22°C and Et=800 W/m²:
U1=+/-0.056 (+/-5.6% relative)
and
U2=+/-0.048 (+/-4.8% relative)
The measurement uncertainty is calculated in accordance with EAL R2.
SP Sweden’s Testing and Research Institute
Energy technology, System and ventilation technology
Appendices
- Technical description of the solar collector with help of data provided by the client
- Discovery of the solar collector’s thermal characteristics – results
- Stagnation and shock test
Page 1(2) – Appendix 1
Technical description of the solar collector with information provided by the client
Manufacturer: Texsun AB
Version: Object nr 2 sent to SP
External dimensions: 1430 x 575 mm (w x h) – 3 units provided
Pipe connection: ½” pipe thread
Page 2(2) – Appendix 1
Photo taken during test
Page 1(10) – Appendix 2
Determination of the solar collector’s thermal characteristics
Determination of thermal characteristics means that the solar collector’s effective level of efficiency is determined, partly without losses (n0) and partly in situations of excess temperature. In addition the solar collector’s thermal loss coefficients k0 and k1 are determined. The measurements are made in accordance with method NT VVS 004 (SP-C12-301).
Performance of the tests
The measurements were performed in SP Energy Technology’s solar simulator. The solar collector was mounted at a 45° angle, directly facing the main stream of light from the simulator. Both n0 (efficiency without losses) and the efficiency in situations of excess temperature were determined through measurements with the solar simulator light and irradiation of >800 W/m² at the solar collector’s surface. One of the measurements was performed “wind free” while for two of the measurements fans were used to blow towards the solar collector’s surface at a speed of 1.7 m/s and 3.4 m/s respectively.
The underlying surface for the collectors was a wooden platform painted with dull white paint and a U-value of approx. 1 W/m².
A correction factor based on the measurements in the simulator has been included in the calculations to make allowance for the heightened level of irradiation that efficiency measurements in the simulator entail in comparison with outdoor measurements. This correction factor is applied similarly to all measurements of unglazed solar collectors and means that 7.5% is added to the measured (short-wave) irradiation, which is equivalent to the amount of measured long-wave radiation.
The stagnation test was performed on non-chilled solar collectors without wind effect.
Operating data during efficiency/loss measurements:
Heat conductor: Water
Flow: 0.02 kg/s x m²
Pressure: 40 – 45 kPa additional pressure at the inlet to the collectors.
Results
Measurement data in table form + calculated results - See pages 2, 3, 4
Efficiency, diagram - See pages 5, 6
Heat losses, diagram - See page 7
Loss coefficient, diagram - See page 8
Annual production - See page 9
Glossary - See page 10
Page 2(10) – Appendix 2
Results Texsun collector at 0 m/s
Measurement data and calculated data.
In the table the average value for each measuring series is given.
The headings for the table (under which the measured data at different temperatures is recorded) are:
- Irradiation W/m²
- Volume flow l/s
- TL (air temperature) °C
- In-temp °C
- Temp-diff °C
- TF-TL (average temp. of water in solar collector minus air temperature) °C
- Efficiency %
Summary of empirical data at bottom of table:
n0 = 80.7 % Wind = 0 m/s
k0 = 13.46 W/(m² °C) Ref area = 2.47 m²
k1 = 0.096 W/(m² °C²)
ke (20) = 15.38 W/(m² °C)
Equation for solar collector’s efficiency rating: n = n0-k0 / Et x (TF – TL) – k1/Et x (TF – TL)²
Equation for solar collector’s loss coefficient: ke = k0 + k1 x (TF – TL)
Equation for solar collector’s losses: Pf / Ag = ke x (TF – TL)
Where:
n = efficiency
TF = heat conductor’s average temperature (°C)
TL = surrounding air temperature
Ag = aperture- (glazed) area (m²)
Et = irradiation (W/m²)
Page 3(10) – Appendix 2
Results Texsun collector at 1.7 m/s
Measurement data and calculated data.
In the table the average value for each measuring series is given.
The headings for the table (under which the measured data at different temperatures is recorded) are:
- Irradiation W/m²
- Volume flow l/s
- TL (air temperature) °C
- In-temp °C
- Temp-diff °C
- TF-TL (average temp. of water in solar collector minus air temperature) °C
- Efficiency %
Summary of empirical data at bottom of table:
n0 = 76.6 % Wind = 1.7 m/s
k0 = 23.45 W/(m² °C) Ref area = 2.47 m²
k1 = 0.079 W/(m² °C²)
ke (15) = 24.64 W/(m² °C)
Equation for solar collector’s efficiency rating: n = n0-k0 / Et x (TF – TL) – k1/Et x (TF – TL)²
Equation for solar collector’s loss coefficient: ke = k0 + k1 x (TF – TL)
Equation for solar collector’s losses: Pf / Ag = ke x (TF – TL)
Where:
n = efficiency
TF = heat conductor’s average temperature (°C)
TL = surrounding air temperature
Ag = aperture- (glazed) area (m²)
Et = irradiation (W/m²)
Page 4(10) – Appendix 2
Results Texsun collector at 3.4 m/s
Measurement data and calculated data.
In the table the average value for each measuring series is given.
The headings for the table (under which the measured data at different temperatures is recorded) are:
- Irradiation W/m²
- Volume flow l/s
- TL (air temperature) °C
- In-temp °C
- Temp-diff °C
- TF-TL (average temp. of water in solar collector minus air temperature) °C
- Efficiency %
Summary of empirical data at bottom of table:
n0 = 72.2 % Wind = 3.4 m/s
k0 = 34.57 W/(m² °C) Ref area = 2.47 m²
k1 = 0.052 W/(m² °C²)
ke (10) = 35.09 W/(m² °C)
Equation for solar collector’s efficiency rating: n = n0-k0 / Et x (TF – TL) – k1/Et x (TF – TL)²
Equation for solar collector’s loss coefficient: ke = k0 + k1 x (TF – TL)
Equation for solar collector’s losses: Pf / Ag = ke x (TF – TL)
Where:
n = efficiency
TF = heat conductor’s average temperature (°C)
TL = surrounding air temperature
Ag = aperture- (glazed) area (m²)
Et = irradiation (W/m²)
Page 5(10) – Appendix 2
Shows a graph displaying measured values at Et (irradiation) = 800 W/m²; and with varying wind speeds 0 m/s, 1.7 m/s and 3.4 m/s.
The x-axis = TF – TL (°c) [Average temperature of water in collector minus air temperature]
The y-axis = Efficiency %
The graph (diagram 1) displays: Thermal efficiency vs. mean temperature above ambient.
Equation for solar collector’s efficiency rating: n = n0-k0 / Et x (TF – TL) – k1/Et x (TF – TL)²
Et = 800 W/m²
n0 = 80.7 / 76.6 / 72.2 %
k0 = 13.46 / 23.45 / 34.57 W/(m² x °C)
k1 = 0.096 / 0.079 / 0.052 W/(m² x °C²)
Page 6(10) – Appendix 2
Shows a graph displaying measured values at Et (irradiation) = 800 W/m²; and with varying wind speeds 0 m/s, 1.7 m/s and 3.4 m/s.
The x-axis = TF – TL / Et [m² x °C/W]
The y-axis = Efficiency %
The graph (diagram 2) displays: Thermal efficiency vs. mean temperature above ambient divided by irradiance.
Equation for solar collector’s efficiency rating: n = n0-k0 (TF – TL) / Et – k1Et ((TF – TL) / Et)²
Et = 800 W/m²
n0 = 80.7 / 76.6 / 72.2 %
k0 = 13.46 / 23.45 / 34.57 W/(m² x °C)
k1 = 0.096 / 0.079 / 0.052 W/(m² x °C²)
Page 7(10) – Appendix 2
The x-axis = TF – TL [°C]
The y-axis = PF / Ag [W/m²]
The graph (diagram 3) displays thermal losses (PF) per unit area (Ag) vs. mean temperature above ambient.
Equation for solar collector’s losses: PF / Ag = k0 (TF – TL) + k1 (TF – TL)²
k0 = 13.46 / 23.45 / 34.57 W/(m² x °C)
k1 = 0.096 / 0.079 / 0.052 W/(m² x °C²)
Page 8(10) – Appendix 2
The x-axis = TF – TL [°C]
The y-axis = ke [W/(m² x °C)]
The graph (diagram 4) displays heat loss coefficient (ke) vs. mean temperature above ambient.
Equation for effective loss coefficient: ke = k0 + k1 (TF – TL)
k0 = 13.46 / 23.45 / 34.57 W/(m² x °C)
k1 = 0.096 / 0.079 / 0.052 W/(m² x °C²)
Page 9(10) – Appendix 2
Annual yield
The annual yield is calculated for the solar collector facing towards the sun at a 45° angle to horizontal. The weather data concerns Stockholm, Sweden 1986. The yield is calculated with help of the simulation programme Minsun (version 910905) and is based on the Swedish Test and Research Institute’s test results, from test protocol nr. P1 00818_2 / date 2001-04-25.
The temperatures given relate to the average temperature in the solar collector.
| Total available yield | Annual yield [kWh / m²] | Reference area |
| 1062 kWh | (for wind speed 0 / 1.7 / 3.4 m/s) | during test [m²] |
| Yield at 15 °C | 722 / 676 / 656 | 2.47 |
| Yield at 25 °C | 433 / 293 / 199 | 2.47 |
| Yield at 35 °C | 234 / 96 / 31 | 2.47 |
Please note that these figures are calculated primarily for the purpose of comparison and that the actual yield from a system will depend, not only on available solar irradiation, but also on system design, placement of the solar collectors, correct maintenance and use, etc.
Page 10(10) – Appendix 2
Glossary of symbols and terms
| Symbol | Description | Unit |
| Ag | The solar collector’s visible frontal area | m² |
| cp | The heat conductor’s specific isobaric heating capacity | J/(kg x K) |
| Et | Total solar irradiation at the solar collector’s surface | W/m² |
| ke | The solar collector’s effective loss coefficient | W/(m²K) |
| k0, k1 | Effective loss coefficients depending on excess temperature ke = k0 + k1 (TF – TL) |
|
| qm | Mass flow | kg/s |
| PF | The solar collector’s heat loss | W |
| TL | The ambient temperature, the air temperature | °C, K |
| Tin | The heat conductor’s inlet temperature | °C, K |
| Tut | The heat conductor’s outlet temperature | °C, K |
| TF | The heat conductor’s average temperature inside the solar collector: TF = (Tin + Tut)/2 |
°C, K |
| n | The solar collector’s thermal efficiency | |
| n0 | The solar collector’s thermal efficiency without losses |
Page 1(1) – Appendix 3
Stagnation test
The test was performed indoors in SP Energy Technology’s solar simulator with the solar collector pointed directly towards the falling light and at a 45° angle.
The purpose of the test is to check that the solar collector, at least during a short period of time, is able to handle the maximum temperature that can be achieved with full solar irradiation and stagnation in the solar collector.
Test object
Solar collector from Texsun, version nr. 2.
Observations
Damages to the collector = nothing observable.
The level of irradiation during the test was 1030 W/m².
Stagnation temperature 63 °C with ambient (air) temperature 20 °C and wind speed 0 m/s.
The stagnation temperature was measured with a thermal element in a channel approx. 200 mm from the top.
On the back side of the collector a temperature of 55 °C was measured.